1. Field of the Invention
This invention relates generally to motor vehicle powertrain control, and, in particular, to correcting indicated engine output torque for use in transmission control.
2. Description of the Prior Art
Vehicle manufacturers use diesel emission treatment equipment in order to comply with more stringent diesel emissions control requirements. For example, diesel particulate filters (DPF) are now used to comply with updated emissions standards. These filters are cleaned or regenerated periodically by raising the temperature of engine exhaust gas, which oxidizes the soot and ash in the filter as the exhaust gas flows through the DPF.
The DPF regeneration process occurs in three modes: Mode 0 is base, non-regenerative operation, mode 1 pre-heats the exhaust close to the required regenerative temperature, and in mode 2 the exhaust is hot enough for the regenerative cycle to terminate after the particulates in the DPF oxidize.
Each mode of the regenerative process has a unique engine torque map. Moving from one mode to another can cause large variations in engine output torque. These large variations present a problem with respect to control of an automatic transmission located in a vehicle powertrain with a diesel engine having a DPF. For example, a base (mode 0) engine mapping error of +5% at 500 ft-lb is a +25 ft-lb torque error. A mode 1 engine mapping error of −5% at 500 ft-lb is a −25 ft-lb torque error.
The transmission controls, which are calibrated to the base mapping error, might not handle a possible ±50 ft-lb difference in the torque error from base when the engine transitions in and out of the regenerative process. Additionally, the existing adaptive pressure control algorithms will hunt from poor to good shifts each time the regenerative process is entered and exited as the algorithms accommodate to the unique torque maps.
Though it is possible to reduce the torque error through better mapping, it is difficult, if not impossible, to completely eliminate when hardware variability is taken into account. For example, fuel injectors have part-to-part variability, including aging, and the base torque map may change over time. Normally, pressure control adaptive compensates for these effects. However, aging may have a completely different effect on the particulate filter regeneration torque map because the fueling pulses are not the same. Thus the traditional pressure control adaptive is unable to compensate for both modes of engine operation.